tt has 8 distinct synonyms spread across 3 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
(astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions
a republic in the western central Pacific Ocean in association with the United States
a country scattered over Micronesia with a constitutional government in free association with the United States; achieved independence in 1986
Synonyms, antonyms and the broader and narrower relations for tt come from Princeton University’s WordNet. Full sources and licences.